From fcaf7595dbec8c30d2107b07ac8a9e3ce21c4bc1 Mon Sep 17 00:00:00 2001
From: Matthew Gretton-Dann <matt@gretton-dann.org.uk>
Date: Sun, 12 Dec 2021 08:02:35 +0000
Subject: [PATCH] Add 2021 day 12 puzzles

---
 2021/puzzle-12-01.cc | 76 +++++++++++++++++++++++++++++++++++
 2021/puzzle-12-02.cc | 94 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 170 insertions(+)
 create mode 100644 2021/puzzle-12-01.cc
 create mode 100644 2021/puzzle-12-02.cc

diff --git a/2021/puzzle-12-01.cc b/2021/puzzle-12-01.cc
new file mode 100644
index 0000000..46f91c8
--- /dev/null
+++ b/2021/puzzle-12-01.cc
@@ -0,0 +1,76 @@
+//
+// Created by Matthew Gretton-Dann on 12/12/2021.
+//
+
+#include <cctype>
+#include <iostream>
+#include <map>
+#include <string>
+#include <vector>
+
+using Paths = std::multimap<std::string, std::string>;
+using Route = std::vector<std::string>;
+
+auto is_upper_case(std::string const& s) -> bool { return std::isupper(s[0]) ? true : false; }
+
+auto is_visitable(Route const& route, Paths const& paths, std::string const& proposed) -> bool
+{
+  if (is_upper_case(proposed)) {
+    return true;
+  }
+  auto route_it = std::find(route.begin(), route.end(), proposed);
+  return route_it == route.end();
+}
+
+template<typename Fn>
+void visit(Route& route, Paths const& paths, Fn visitor)
+{
+  auto [path_begin, path_end] = paths.equal_range(route.back());
+  if (path_begin == path_end) {
+    visitor(route, paths);
+    return;
+  }
+
+  for (auto it{path_begin}; it != path_end; ++it) {
+    if (is_visitable(route, paths, it->second)) {
+      route.push_back(it->second);
+      visit(route, paths, visitor);
+      route.pop_back();
+    }
+  }
+}
+
+auto main() -> int
+{
+  Paths paths;
+  std::string line;
+  while (std::getline(std::cin, line)) {
+    auto sep{line.find('-')};
+    auto from{line.substr(0, sep)};
+    auto to{line.substr(sep + 1)};
+
+    // Make sure we don't visit start or end more than once.
+    if (to == "start") {
+      std::swap(from, to);
+    }
+    if (from == "end") {
+      std::swap(from, to);
+    }
+    paths.insert({from, to});
+    if (from != "start" && to != "end") {
+      paths.insert({to, from});
+    }
+  }
+
+  unsigned route_count{0};
+  Route route{"start"};
+  visit(route, paths, [&route_count](auto const& route, auto const&) {
+    for (auto r : route) {
+      std::cout << " " << r;
+    }
+    std::cout << "\n";
+    ++route_count;
+  });
+  std::cout << "Routes count: " << route_count;
+  return 0;
+}
diff --git a/2021/puzzle-12-02.cc b/2021/puzzle-12-02.cc
new file mode 100644
index 0000000..44d1417
--- /dev/null
+++ b/2021/puzzle-12-02.cc
@@ -0,0 +1,94 @@
+//
+// Created by Matthew Gretton-Dann on 12/12/2021.
+//
+
+#include <cctype>
+#include <iostream>
+#include <map>
+#include <set>
+#include <string>
+#include <vector>
+
+using Paths = std::multimap<std::string, std::string>;
+using Route = std::vector<std::string>;
+
+auto is_upper_case(std::string const& s) -> bool { return std::isupper(s[0]) ? true : false; }
+
+auto is_visitable(Route const& route, Paths const& paths, std::string const& proposed) -> bool
+{
+  if (is_upper_case(proposed)) {
+    return true;
+  }
+
+  std::set<std::string> visited;
+  bool little_visited_twice{false};
+  for (auto r : route) {
+    if (!is_upper_case(r)) {
+      if (visited.contains(r)) {
+        little_visited_twice = true;
+        break;
+      }
+      visited.insert(r);
+    }
+  }
+
+  if (!little_visited_twice) {
+    return true;
+  }
+
+  auto route_it = std::find(route.begin(), route.end(), proposed);
+  return route_it == route.end();
+}
+
+template<typename Fn>
+void visit(Route& route, Paths const& paths, Fn visitor)
+{
+  auto [path_begin, path_end] = paths.equal_range(route.back());
+  if (path_begin == path_end) {
+    visitor(route, paths);
+    return;
+  }
+
+  for (auto it{path_begin}; it != path_end; ++it) {
+    if (is_visitable(route, paths, it->second)) {
+      route.push_back(it->second);
+      visit(route, paths, visitor);
+      route.pop_back();
+    }
+  }
+}
+
+auto main() -> int
+{
+  Paths paths;
+  std::string line;
+  while (std::getline(std::cin, line)) {
+    auto sep{line.find('-')};
+    auto from{line.substr(0, sep)};
+    auto to{line.substr(sep + 1)};
+
+    // Make sure we don't visit start or end more than once.
+    if (to == "start") {
+      std::swap(from, to);
+    }
+    if (from == "end") {
+      std::swap(from, to);
+    }
+    paths.insert({from, to});
+    if (from != "start" && to != "end") {
+      paths.insert({to, from});
+    }
+  }
+
+  unsigned route_count{0};
+  Route route{"start"};
+  visit(route, paths, [&route_count](auto const& route, auto const&) {
+    for (auto r : route) {
+      std::cout << " " << r;
+    }
+    std::cout << "\n";
+    ++route_count;
+  });
+  std::cout << "Routes count: " << route_count;
+  return 0;
+}